What is the speed of gravity?

Turkey · December 23, 2015, 11:15:45 PM

Quote

If the sun disappeared instantly, when would we stop feeling its gravity?

This came up in a discussion with some non-science-type friends, and I thought it'd be interesting to discuss. The short answer is that gravity works at the speed of light. The long answer is that Einstein's Theory of Relativity assumed that gravity propagates at the speed of light (despite having no real way to measure this), so scientists used it until the past decade when astronomers were able to compare gravity distortions from Jupiter and determined that the speed of gravity is within 70%-120% of the speed of light (with the speed of light being the mean answer); it was tantamount to proof that the speed of light and gravity are one and the same.

So what are the consequences or implications of this? Nothing, really. There's no reason establish a connection between light and gravity; i.e., gravity isn't propagated by light. But what we can understand is that the speed of light isn't specific to light, it's actually a universal constant of any massless particle -- basically the speed of light is the absolute limit for any information or interaction in the universe. What else does that mean? If gravity really is a result of an interaction between standard particles and some gravity particle -- the 'graviton' -- then it is completely massless, like a photon.

Competing theories to Relativity are String Theory and Multiverse Theory. In String Theory, there may exist another dimension (not universe, but a spacial dimension) that can (but doesn't typically) propagate gravity at a speed other than c. There's a whole lot more to it than that, but the point is that Relativity isn't the only kid on the block. That being said, String/Multiverse theory is basically math-based theology, and neither are accepted in any scientific field nor is there a unified set of axioms for any variation of those theories.

I hope you learned something, and if there's anything weird you'd like to learn about in the future, post it here.

Further reading:

http://www.universetoday.com/121284/how-fast-is-gravity/

https://en.wikipedia.org/wiki/Brane

http://www.desy.de/user/projects/Physics/Relativity/GR/grav_speed.html

DAS B00T x2 · December 23, 2015, 11:18:46 PM

It it bad that my first thought upon reading the title was "9.8 meters per second"?

SecondClass · December 23, 2015, 11:19:39 PM

Doesn't it depend on the object being dropped? I don't think it's a constant.

Again, I have literally zero knowledge on this subject, so I'm probably wrong.

Turkey · December 23, 2015, 11:21:34 PM

Quote from: SecondClass on December 23, 2015, 11:19:39 PM

Doesn't it depend on the object being dropped? I don't think it's a constant.

I think you're referring to the force of gravity, 9.8 meters per second per second, which is still a constant. The OP is about how fast gravity affects something; for example, if the sun disappeared instantly we'd feel the loss of its gravity at exactly the same time we lose its light.

DAS B00T x2 · December 23, 2015, 11:22:18 PM

Quote from: SecondClass on December 23, 2015, 11:19:39 PM

Doesn't it depend on the object being dropped? I don't think it's a constant.

Again, I have literally zero knowledge on this subject, so I'm probably wrong.

Nah, I'm pretty sure it's constant and will appear as such unless an outside force such as friction or air resistance is working against it.

SecondClass · December 23, 2015, 11:22:28 PM

Quote from: The Turkey Awakens on December 23, 2015, 11:21:34 PM

Quote from: SecondClass on December 23, 2015, 11:19:39 PM
Doesn't it depend on the object being dropped? I don't think it's a constant.

I think you're referring to the force of gravity, 9.8 meters per second per second, which is still a constant. The OP is about how fast gravity affects something; for example, if the sun disappeared instantly we'd feel the loss of its gravity at exactly the same time we lose its light.

Oh, that makes sense.

More Than Mortal · December 23, 2015, 11:22:43 PM

I thought photons were almost totally massless.

DAS B00T x2 · December 23, 2015, 11:23:00 PM

Quote from: The Turkey Awakens on December 23, 2015, 11:21:34 PM

Quote from: SecondClass on December 23, 2015, 11:19:39 PM
Doesn't it depend on the object being dropped? I don't think it's a constant.

I think you're referring to the force of gravity, 9.8 meters per second per second, which is still a constant. The OP is about how fast gravity affects something; for example, if the sun disappeared instantly we'd feel the loss of its gravity at exactly the same time we lose its light.

Whoa.

That's pretty fucking cool.

Sandtrap · December 23, 2015, 11:23:46 PM

This is something I talked about with a friend a while back. In theory, gravity obeys einstien's nice old math equation.

For instance, if the sun suddenly where to dissappear entirely, it would take 8 minutes for our planet to stop continuing on its normal track before it was flung straight ahead in the most relevant direction. And, as we were flying away, the further planets in our system would still be there for about 18 hours, ending with Pluto, before every last planet was flung away completely due to the loss of the gravitational center of our cluster.

It's spooky to think about, really. Everything is held in balance and yet it's not an instantaneous force even though it's a constant force.

Sandtrap · December 23, 2015, 11:24:30 PM

Quote from: The Meta Order on December 23, 2015, 11:22:43 PM

I thought photons were almost totally massless.

So close to zero that they're considered zero.

Turkey · December 23, 2015, 11:25:26 PM

Quote from: The Meta Order on December 23, 2015, 11:22:43 PM

I thought photons were almost totally massless.

In special relativity, photons are assumed to be massless because they only partially behave as particles. Even if they did have mass, their mass would be so astronomically negligible that it would be completely insignificant.

Kiwicake · December 23, 2015, 11:25:55 PM

Quote from: SecondClass on December 23, 2015, 11:19:39 PM

Doesn't it depend on the object being dropped? I don't think it's a constant.

Again, I have literally zero knowledge on this subject, so I'm probably wrong.

How much you accelerate due to gravity has nothing to do with the object, that's caused by things like air resistance (At least on Earth), which is constant

But he's talking about the speed at which the gravity from a body of mass will begin to affect you, you're being influenced by gravity from the sun and the moon too, and technically every body of mass around you. But the speed at which gravity propagates is what we're talking about here

More Than Mortal · December 23, 2015, 11:26:29 PM

Quote from: Snowtrap on December 23, 2015, 11:24:30 PM

Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

So close to zero that they're considered zero.

So couldn't information which is literally massless travel faster than c? Or is there some universal barrier preventing anything from being any more massless than a photon or graviton?

Sandtrap · December 23, 2015, 11:32:02 PM

Quote from: The Meta Order on December 23, 2015, 11:26:29 PM

Quote from: Snowtrap on December 23, 2015, 11:24:30 PM
Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

So close to zero that they're considered zero.
So couldn't information which is literally massless travel faster than c? Or is there some universal barrier preventing anything from being any more massless than a photon or graviton?

Information technically has mass as well because it is stored in something or requires something physical to.... create it, I guess.

Computers use electrons, our brains use natural electrical currents and all that. Information does have a speed limit which obeys the speed of light that we currently know of.

If we ever found information that could travel faster than light, well, we probably wouldn't even be able to process it or even acknowledge its existence.

Turkey · December 23, 2015, 11:32:54 PM

Quote from: The Meta Order on December 23, 2015, 11:26:29 PM

Quote from: Snowtrap on December 23, 2015, 11:24:30 PM
Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

So close to zero that they're considered zero.
So couldn't information which is literally massless travel faster than c? Or is there some universal barrier preventing anything from being any more massless than a photon or graviton?

Photons are literally massless in terms of traditional physics. In special relativistic terms you could assign the particle some mass, but it wouldn't be at all the equivalent of mass we normally talk about. That probably didn't clear it up, sorry.

As for information, don't think of it like computers, which use electrons and storage. True information is a basic reaction between particles. So in the example of the sun disappearing, that information would be conveyed by the loss of gravity, light, and heat. For any information to travel faster than c, a particle conveying that information would have to move faster than c.

Sandtrap · December 23, 2015, 11:36:24 PM

Quote from: The Turkey Awakens on December 23, 2015, 11:32:54 PM

Quote from: The Meta Order on December 23, 2015, 11:26:29 PM
Quote from: Snowtrap on December 23, 2015, 11:24:30 PM
Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

So close to zero that they're considered zero.
So couldn't information which is literally massless travel faster than c? Or is there some universal barrier preventing anything from being any more massless than a photon or graviton?

Photons are literally massless in terms of traditional physics. In special relativistic terms you could assign the particle some mass, but it wouldn't be at all the equivalent of mass we normally talk about. That probably didn't clear it up, sorry.

As for information, don't think of it like computers, which use electrons and storage. True information is a basic reaction between particles. So in the example of the sun disappearing, that information would be conveyed by the loss of gravity, light, and heat. For any information to travel faster than c, a particle conveying that information would have to move faster than c.

I was going to use the board analogy but I skipped it.

Assassin 11D7 · December 23, 2015, 11:45:07 PM

Quote from: The Turkey Awakens on December 23, 2015, 11:25:26 PM

Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

In special relativity, photons are assumed to be massless because they only partially behave as particles. Even if they did have mass, their mass would be so astronomically negligible that it would be completely insignificant.

Even in something like quantum mechanics/physics, where they work with incredibly small factors?

Flee · December 24, 2015, 01:19:57 AM

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Cadenza has moved on · December 24, 2015, 04:10:28 AM

Quote from: The Turkey Awakens on December 23, 2015, 11:15:45 PM

basically the speed of light is the absolute limit for any information or interaction in the universe.

I've been wondering about this before, It's fascinating stuff that I look forward to studying.

BaconShelf · December 24, 2015, 04:29:07 AM

Quote from: DAS THE HALLS on December 23, 2015, 11:18:46 PM

It it bad that my first thought upon reading the title was "9.8 meters per second"?

Yes it is.

It should have been 9.8ms^2

BaconShelf · December 24, 2015, 04:37:24 AM

Quote from: The Meta Order on December 23, 2015, 11:26:29 PM

Quote from: Snowtrap on December 23, 2015, 11:24:30 PM
Quote from: The Meta Order on December 23, 2015, 11:22:43 PM
I thought photons were almost totally massless.

So close to zero that they're considered zero.
So couldn't information which is literally massless travel faster than c? Or is there some universal barrier preventing anything from being any more massless than a photon or graviton?

It's not just to do with the masses. As you accelerate, your perception of time changes so that you alsp experience time quicker in relation to everything else. At C, time around you stops completely. In effect, hitting lightspeed means that before you'd have even begun an instant of travel at lightspeed, you would have lived for an infinite amount of time. If you were theoretically able to achieve a higher velocity, then time would start to go backwards in relation to you.

Mass and energy aren't the only factors as to C is the limit. I guess it's not really directly related to your question but a cool tidbit either way.

As for the question itself, there's nothing theoretically stopping something having less mass than a photon (Gravitons haven't been discovered, just theorised). We just haven't discovered anything on that scale yet.

BaconShelf · December 24, 2015, 04:39:16 AM

OT- I didn't really learn anything new with the OP. Nonetheless,,physics is a fascinating topic. I love being able to discuss it.

Flee · December 24, 2015, 04:49:03 AM

This user has been blacklisted from posting on the forums. Until the blacklist is lifted, all posts made by this user have been hidden and require a Sep7agon^® SecondClass Premium Membership to view.

More Than Mortal · December 24, 2015, 05:10:22 AM

Quote from: Flee on December 24, 2015, 04:49:03 AM

Quote from: space boy on December 24, 2015, 04:29:07 AM
Quote from: DAS THE HALLS on December 23, 2015, 11:18:46 PM
It it bad that my first thought upon reading the title was "9.8 meters per second"?

Yes it is.

It should have been 9.8ms^2
What's wrong with you? It's 9.81.

I think you mean 32.174.

BaconShelf · December 24, 2015, 05:11:54 AM

Quote from: Flee on December 24, 2015, 04:49:03 AM

Quote from: space boy on December 24, 2015, 04:29:07 AM
Quote from: DAS THE HALLS on December 23, 2015, 11:18:46 PM
It it bad that my first thought upon reading the title was "9.8 meters per second"?

Yes it is.

It should have been 9.8ms^2
What's wrong with you? It's 9.81.

Blame being on a phone and missing the key

DAS B00T x2 · December 24, 2015, 05:35:32 AM

Quote from: Flee on December 24, 2015, 04:49:03 AM

Quote from: space boy on December 24, 2015, 04:29:07 AM
Quote from: DAS THE HALLS on December 23, 2015, 11:18:46 PM
It it bad that my first thought upon reading the title was "9.8 meters per second"?

Yes it is.

It should have been 9.8ms^2
What's wrong with you? It's 9.81.

or is it really 9.11?

Mordo · December 24, 2015, 05:38:38 AM

This is some heavy shit for a Christmas Eve post.

BaconShelf · December 24, 2015, 05:57:19 AM

Quote from: DAS THE HALLS on December 24, 2015, 05:35:32 AM

Quote from: Flee on December 24, 2015, 04:49:03 AM
Quote from: space boy on December 24, 2015, 04:29:07 AM
Quote from: DAS THE HALLS on December 23, 2015, 11:18:46 PM
It it bad that my first thought upon reading the title was "9.8 meters per second"?

Yes it is.

It should have been 9.8ms^2
What's wrong with you? It's 9.81.
or is it really 9.11?

Jet fuel can't melt photon beams

Naru · December 24, 2015, 06:23:06 PM

I love you

Desty · December 25, 2015, 01:11:54 PM

So what you're saying is that if a planet were destroyed a long time ago in a galaxy far, far away, it'd take time before we felt a disturbance in the force?